Heat exchanging device and water heater using the same

ABSTRACT

A heat exchanging device, for performing a heat exchange between a first fluid and a second fluid is provided, includes a first pipe and a second pipe. The first pipe includes a first inlet and a first outlet thereby allowing the first fluid to flow in and out the first pipe through the first inlet and the first outlet, respectively. The second pipe includes a second inlet and a second outlet thereby allowing the second fluid to flow in and out the second pipe through the second inlet and the second outlet, respectively. The first pipe and the second pipe are contacted with each other by being disposed in a juxtaposition manner; and a flowing direction of the first fluid in the first pipe is opposite to a flowing direction of the second fluid in the second pipe. A water heater using the heat exchanging device is also provided.

FIELD OF THE INVENTION

The present invention relates to a heat exchanging device, and more particularly to a heat exchanging device configured to perform a heat exchange between two kinds of fluid. The present invention further relates to a water heater which uses the aforementioned heat exchanging device.

BACKGROUND OF THE INVENTION

Heat pump water heater is for heating cold water into hot water by sequentially using heat medium (i.e., refrigerant) to collect heat in air, using a heat pump (i.e., compressor) to pressurize and store the heat medium collected with heat, and then performing a heat exchange between the heat medium and the cold water. Because the heat exchange process in the heat pump water heater is realized by using the refrigerant as the medium for the energy conversion, in theory the energy conversion efficiency can reach to 300% or even above. Thus, compared with the heat exchanges, those use electricity or fire power for the energy conversion, having energy conversion efficiencies lower than 100%, the heat pump water heater can have higher heating efficiency by using limited electricity power. Consequentially, the heat pump water heater is regarded as one of the most environmentally friendly and most power saving equipments capable of resulting significant economic benefits as well as generating much less pollution.

FIG. 1 is a perspective schematic view of a conventional heat pump water heater. As shown, the conventional heat pump water heater includes a compressor 1, a heat exchanger 2, an expansion valve 3 and an evaporator 4. Basically, the conventional heat pump water heater of FIG. 1 has a heat exchange process as follow: firstly, the compressor 1 pressurizes the refrigerant into high-temperature-and-high-pressure gaseous refrigerant; then, the compressor 1 supplies the high-temperature-and-high-pressure gaseous refrigerant into the heat exchanger 2 as a heat medium; then, the high-temperature-and-high-pressure gaseous refrigerant releases heat by exchanging heat thereof with the cold water thereby heating the cold water and condensing the high-temperature-and-high-pressure gaseous refrigerant; then, the expansion valve 3 converts the condensed refrigerant into the gas-liquid mixture refrigerant by using the pressure difference between the high and low pressures; then, the refrigerant absorbs the external heat through the evaporator 4 and the compressor 1 pressurizes the refrigerant into the high temperature-and-high-pressure gaseous refrigerant again. Thus, the flowing water can be heated in the heat exchanger 2 by repeating the aforementioned heat exchange process.

According to the aforementioned description, it is understood that the heat exchange process of a conventional heat pump water heater can be summarized to: the high-temperature-and-high-pressure gaseous refrigerant is condensed in the heat exchanger, and then condensed refrigerant is pressurized into the high temperature-and-high-pressure gaseous refrigerant for the next-time heat exchange. However, it is understood that during the process for storing heat, the refrigerant's heat energy includes latent heat and sensible heat, and conventionally the latent heat and the sensible heat stored in the refrigerant cannot be completely absorbed by the cold water in the heat exchange once the cold water and the refrigerant reach to the same temperature.

For example, if the cold water is about 25° C. and the refrigerant is about 70-100° C. in an initial period of the heat exchange, the cold water can rapidly absorb heat from the refrigerant and has a rapidly-increasing temperature. Once the water and the refrigerant reach to the same temperature (for example, 55° C.), the refrigerant no longer releases heat and the water cannot be heated anymore.

In other words, in the conventional heat pump water heater, the cold water does not absorb the all heat stored in the refrigerant; specifically, the cold water does not absorb the latent heat part stored in the refrigerant. That is because the refrigerant has not reached to the temperature capable of releasing the latent heat (the heat energy released during gas is being converted into liquid) when the refrigerant and the cold water reach to the same temperature. As a result, the temperature of the heated water is limited and cannot be further increased. Currently, the temperature of the heated water flowing out from the conventional heat pump water heater is about 55° C., which is an serious issue to be overcome.

SUMMARY OF THE INVENTION

One aspect of the present invention is to provide a heat exchanging device having improved heat exchanger efficiency.

Another aspect of the present invention is to provide a water heater having improved heat exchanger efficiency.

The present invention provides a heat exchanging device configured to perform a heat exchange between a first fluid and a second fluid. The heat exchanging device includes a first pipe and a second pipe. The first pipe includes a first inlet and a first outlet thereby allowing the first fluid to flow in and out the first pipe through the first inlet and the first outlet, respectively. The second pipe includes a second inlet and a second outlet thereby allowing the second fluid to flow in and out the second pipe through the second inlet and the second outlet, respectively. The first pipe and the second pipe are contacted with each other by being disposed in a juxtaposition manner; and a flowing direction of the first fluid in the first pipe is opposite to a flowing direction of the second fluid in the second pipe.

In one embodiment, both of the first and second pipes are oval-shaped pipes, the first pipe has a first contact surface, the second pipe has a second contact surface, the first contact surface and the second contact surface are contacted with each other in an extending direction of a short axis of each oval-shaped pipe.

In one embodiment, both of the first and second pipes are polygon-shaped pipes, the first pipe has a first contact surface, the second pipe has a second contact surface, the first contact surface and the second contact surface are contacted with each other.

In one embodiment, the first pipe has a first contact surface, the second pipe has a second contact surface, the first contact surface and the second contact surface are contacted with each other, the first contact surface has at least a recess, the second contact surface has at least a protrusion, the recess and the protrusion are contacted with each other.

In one embodiment, the first pipe has a first contact surface, the second pipe has a second contact surface, the first contact surface and the second contact surface are contacted with each other, the first contact surface has at least a protrusion, the second contact surface has at least a recess, the recess and the protrusion are contacted with each other.

In one embodiment, both of the first and second pipes have winding-and-bending structures.

In one embodiment, the aforementioned heat exchanging device further includes an insulating layer configured to wrap the first and second pipes.

In one embodiment, the aforementioned heat exchanging device further includes a container and an insulating layer. The first and second pipes are disposed in the container. The insulating layer is disposed in the container and configured to wrap the first and second pipes.

The present invention further provides a water heater, which includes the heat exchanging device in any one of the aforementioned embodiment and a heating unit. The heating unit is connected between the first outlet and the first inlet of the first pipe of the heat exchanging device.

In one embodiment, the water heater further includes a receptacle configured to receive the second fluid flowing out from the second outlet of the second pipe.

In summary, through configuring the flowing direction of the first fluid in the first pipe opposite to the flowing direction of the second fluid in the second pipe, the heat exchanging device and the water heater of the present invention have improved heat exchanger efficiency.

For making the above and other purposes, features and benefits become more readily apparent to those ordinarily skilled in the art, the preferred embodiments and the detailed descriptions with accompanying drawings will be put forward in the following descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which:

FIG. 1 is a perspective schematic view of a conventional heat pump water heater;

FIG. 2 is a perspective schematic view of a heat exchanging device according to a first embodiment of the present invention;

FIG. 3 is a cross-sectional view of a portion of the heat exchanging device of FIG. 2;

FIG. 4 is a perspective schematic view of a heat exchanging device according to a second embodiment of the present invention;

FIG. 5 is a cross-sectional view of a portion of a heat exchanging device according to a third embodiment of the present invention;

FIG. 6 is a cross-sectional view of a portion of a heat exchanging device according to a fourth embodiment of the present invention;

FIG. 7 is a cross-sectional view of a portion of a heat exchanging device according to a fifth embodiment of the present invention;

FIG. 8 is a cross-sectional view of a portion of a heat exchanging device according to a sixth embodiment of the present invention; and

FIG. 9 is a perspective schematic view of a water heater using the heat exchanging device of FIG. 2 according to an embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed.

FIG. 2 is a perspective schematic view of a heat exchanging device according to a first embodiment of the present invention. FIG. 3 is a cross-sectional view of a portion of the heat exchanging device of FIG. 2. Please refer to FIGS. 2 and 3. The heat exchanging device 100 in the present embodiment is configured to perform a heat exchange between a first fluid F1 and a second fluid F2. The heat exchanging device 100 includes a first pipe 110 and a second pipe 120. The first pipe 110 has a first inlet 112 and a first outlet 114, through which the first fluid F1 can flow in and flow out from the first pipe 110, respectively. The second pipe 120 has a second inlet 122 and a second outlet 124, through which the second fluid F2 can flow in and flow out from the second pipe 120, respectively. The first pipe 110 and the second pipe 120 are contacted with each other by being disposed in a juxtaposition manner. The flowing direction of the first fluid F1 in the first pipe 110 is opposite to the flowing direction of the second fluid F2 in the second pipe 120.

In the first embodiment of the present invention, the first inlet 112 is adjacent to the second outlet 124 and the first outlet 114 is adjacent to the second inlet 122. It is to be noted that the first inlet 112 and the first outlet 114 herein are referred to as the two ends of the first pipe 110; and accordingly the two ends of the first pipe 110 are contacted with the second pipe 120. In one embodiment, each of the first inlet 112 and the first outlet 114 can be further connected to another respective pipe (not shown), and the respective pipe(s) and the first pipe 110 may have one-piece structure. For example, the first inlet 112 can be connected to the supply resource of the first fluid F1 through one respective pipe. Similarly, the second inlet 122 and the second outlet 124 herein are referred to as the two ends of the second pipe 120; and accordingly the two ends of the second pipe 120 are contacted with the first pipe 110. In one embodiment, each of the second inlet 122 and the second outlet 124 can be further connected to another respective pipe (not shown), and the respective pipe(s) and the second pipe 120 may have one-piece structure. For example, the second inlet 122 can be connected to the supply resource of the second fluid F2 through one respective pipe. In one embodiment, both of the first pipe 110 and the second pipe 120 may be cylinder-shaped pipes; however, the first pipe 110 and the second pipe 120 may have other shapes and the present invention is not limited thereto. The materials of the first pipe 110 and the second pipe 120 may have high thermal conductivities, such as metal (e.g. copper), alloy or composite materials.

The process of heat exchange performed by the heat exchanging device 100 of the first embodiment in the present invention will be described as follow by exemplarily referring the first pipe 110 as a heat-source conduction pipe for supplying the heat medium (i.e., the first fluid F1) and referring the second pipe 120 as a heating pipe for supplying cold water (i.e., the second fluid F2).

In this embodiment, the heat contained in the heat medium (the first fluid F1) is transferred to the water (the second fluid F2) sequentially through the first pipe 110 and the second pipe 120. Specifically, because the flowing direction of the first fluid F1 in the first pipe 110 is opposite to the flowing direction of the second fluid F2 in the second pipe 120, the second pipe 120 may be divided into a pre-heating section 126 and a high-temperature section 128 between the second inlet 122 and the second outlet 124 according to the flowing direction of the second fluid F2. Specifically, the pre-heating section 126 is connected to the second inlet 122 and for absorbing the sensible heat contained in the heat medium (the first fluid F1) flowing in the first pipe 110. The high-temperature section 128 is connected to the pre-heating section 126 and for absorbing the latent heat contained in the heat medium (the first fluid F1) flowing in the first pipe 110.

Furthermore, the first pipe 110 may be divided into a latent heat releasing section 116 and a sensible heat releasing section 118 between the first inlet 112 and the first outlet 114 according to the flowing direction of the first fluid F1. Specifically, the latent heat releasing section 116 is connected to the first inlet 112 and corresponding to the high-temperature section 128 of the second pipe 120 for releasing the latent heat contained in the heat medium (the first fluid F1). The sensible heat releasing section 118 is connected to the latent heat releasing section 116 and corresponding to the pre-heating section 126 of the second pipe 120 for releasing the sensible heat contained in the heat medium (the first fluid F1).

According to the flowing direction of the heat medium (the first fluid F1) in the first pipe 110, the heat medium (the first fluid F1) releases the latent heat thereof in the latent heat releasing section 116 of the first pipe 110 and then releases the sensible heat in the sensible heat releasing section 118. Relatively, because the flowing direction of the water (the second fluid F2) is opposite to the flowing direction of the heat medium (the first fluid F1) as described above, the water (the second fluid F2) in the pre-heating section 126 of the second pipe 120 absorbs the sensible heat of the heat medium (the first fluid F1) released in the sensible heat releasing section 118 and then the heated water flowing in the high temperature section 128 further absorbs the latent heat of the heat medium (the first fluid F1) released in the latent heat releasing section 118. Through this configuration, the water (the second fluid F2) can absorb the heat from the heat medium (the first fluid F1) more efficiently during the heat exchange. As a result, compared with the prior art, the heat exchanging device 100 of the present embodiment has improved heat exchange efficiency, the water flowing out from the heat exchanging device 100 can be heated to a higher temperature, and accordingly more energy can be saved.

Moreover, in this embodiment, because that the first pipe 110 and the second pipe 120 are contacted with each other by being disposed in a juxtaposition manner, the first fluid F1 is prevented from flowing into the second pipe 120 thereby polluting the second fluid F2 even when the first pipe 110 is damaged and broken. Similarly, even when the second pipe 120 is damaged and broken, the second fluid F2 is prevented from flowing into the first pipe 110 thereby polluting the first fluid F1.

The first pipe 110 and the second pipe 120 may have straight or winding-and-bending structures; however, the present invention is not limited thereto. In addition, through the winding-and-bending structure, it is understood that more space can be saved under a same heat exchanging distance and the temperature of the water (the second fluid F2) flowing closes to the second outlet 124 of the second pipe 120 (or, the first inlet 112 of the first pipe 110) is close to the initial temperature of the compressed heat medium (the first fluid F1).

FIG. 4 is a perspective schematic view of a heat exchanging device according to a second embodiment of the present invention. As shown, the heat exchanging device 100 a in the second embodiment has a structure similar to that of the heat exchanging device 100 in the first embodiment except that the heat exchanging device 100 a further includes a container 130 and an insulating layer 140; wherein the first pipe 110 and the second pipe 120 are disposed inside of the container 130. The insulating layer 140 is placed in the container 130 and for wrapping the first pipe 110 and the second pipe 120. Thus, the heat loss is prevented from occurring and consequentially the heat exchanging efficiency of the heat exchanging device 100 a is enhanced. In one embodiment, the insulating layer 140 can be foam, foaming agent, air layer or vacuum layer and is filled in the container 130.

FIG. 5 is a cross-sectional view of a portion of a heat exchanging device according to a third embodiment of the present invention. As shown, the heat exchanging device 100 b in the present embodiment has a structure is similar to that of the heat exchanging device 100 in the first embodiment except that the first pipe 110 and the second pipe 120 are wrapped by an insulating layer 150. Thus, the heat loss is prevented from occurring and consequentially the heat exchanging efficiency of the heat exchanging device 100 b is enhanced. In one embodiment, the insulating layer 150 can be foam or foaming agent.

FIG. 6 is a cross-sectional view of a portion of a heat exchanging device according to a fourth embodiment of the present invention. As shown, the heat exchanging device 100 c in the present embodiment has a structure similar to that of the heat exchanging device 100 in the first embodiment except that both of the first pipe 110 c and the second pipe 120 c in the heat exchanging device 100 c are oval-shaped pipes. Specifically, the first pipe 110 c has a first contact surface 111, and the second pipe 120 c has a second contact surface 121 which is contacted with the first contact surface 111. In one embodiment, the first contact surface 111 and the second contact surface 121 are contacted with each other in an extending direction A of the short axis of each oval-shaped pipe. Compared with the heat exchanging device 100 in the first embodiment, the contact area between the first pipe 110 c and the second pipe 120 c is increased and consequentially the heat exchanging efficiency of the heat exchanging device 100 c is further improved.

FIG. 7 is a cross-sectional view of a portion of a heat exchanging device according to a fifth embodiment of the present invention. As shown, the heat exchanging device 100 d in the present embodiment has a structure similar to that of the heat exchanging device 100 in the first embodiment except that both of the first pipe 110 d and the second pipe 120 d in the heat exchanging device 100 d are polygon-shaped pipes, such as square-shaped pipes; however the present invention is not limited thereto. Specifically, the first pipe 110 d has a first contact surface 111, and the second pipe 120 d has a second contact surface 121 which is contacted with the first contact surface 111. Compared with the heat exchanging device 100 in the first embodiment, the contact area between the first pipe 110 d and the second pipe 120 d is increased and the consequentially the heat exchanging efficiency of the heat exchanging device 100 d is further improved.

FIG. 8 is a cross-sectional view of a portion of a heat exchanging device according to a sixth embodiment of the present invention. As shown, the heat exchanging device 100 e in the present embodiment has a structure similar to that of the heat exchanging device 100 in the first embodiment except that the first pipe 110 e in the heat exchanging device 100 c has a first contact surface 111, the second pipe 120 e has a second contact surface 121 which is contacted with the first contact surface 111, the first contact surface 111 has at least one protrusion 113, and the second contact surface 121 has at least one recess 123 which is contacted with the respective protrusion 113. Through the aforementioned structure, the flowing speeds of the first fluid F1 and the second fluid F2 can be slow down by the protrusion(s) 113 and the recess(es) 123 and the time for the heat exchange between the first fluid F1 and the second fluid F2 is increased. As a result, the heat exchanging device 100 e in the present embodiment has improved heat exchanging efficiency.

It is to be noted that the numbers and positions of the protrusion 113 and the recess 123 in the present invention are not limited. In one embodiment, at least one recess is formed on the first contact surface of the first pipe; at least one protrusion is formed on the second contact surface of the second pipe; and the recess is contacted with the respective protrusion.

FIG. 9 is a perspective schematic view of a water heater using the heat exchanging device of FIG. 2 according to an embodiment of the present invention. As shown, the water heater 200 in the present embodiment includes the aforementioned heat exchanging device 100 and a heating unit 210. The heating unit 210 is connected between the first outlet 114 and the first inlet 112 of the heat exchanging device 100.

The heating unit 210 includes an expansion valve 212, an evaporator 214 and a compressor 216, which are sequentially arranged from the first outlet 114 to the first inlet 112. The first outlet 114, the expansion valve 212, the evaporator 214, the compressor 216 and the first inlet 112 sequentially communicate with one another via a pipe 218. Through the corporate operation of the expansion valve 212, the evaporator 214 and the compressor 216, the heat medium (the first fluid F1) is allowed to constantly circulate in the first pipe 210 thereby having the heat exchange with the water (the second fluid F2).

By employing the heat exchanging device 100, accordingly the water heater 200 of this embodiment has improved heat exchange efficiency. According to an experiment, the temperature of the water flowing out from the second outlet 124 of the second pipe 120 can reach to about 70-100° C. For a household use, it is understood that the water heater 200 can be applied to a so-called “tankless water heater” by directly mixing the hot water therein with cold water. For hotels, institutes or dormitories having a higher water quantity demand, it is understood that the water heater 200 can be applied to a so-called “storage water heater” by being equipped with a storage unit 220, which is for receiving and storing the hot water (the second fluid F2) flowing out from the second outlet 124. In one embodiment, the storage unit 220 may include a receptacle 222 for receiving the second fluid F2 flowing out from the second outlet 124. In another embodiment, the storage unit 220 may further include a pipe 224, which is connected to the second outlet 124 and provided for directing the second fluid F2 into the receptacle 222.

Furthermore, because that the first pipe 110 and the second pipe 120 are contacted with each other by being disposed in a juxtaposition manner, the second fluid F2 is prevented from flowing into the heating unit 210 through the first pipe 110 even when the second pipe 120 is damaged and broken; and consequentially the heating unit 210 is prevented from being damaged by the leaking second fluid F2. It is understood that the heat exchanging device 100 in the water heater 200 as shown in FIG. 9 is for exemplary purpose only and can be replaced by any other heat exchanging device disclosed above.

In summary, in the heat exchanging device and the water heater of the present invention, because the flowing direction of the first fluid in the first pipe is opposite to the flowing direction of the second fluid in the second pipe, the second fluid can absorb the sensible heat of the first fluid in the pre-heating section, and then the heated second fluid can further absorb the latent heat of the first fluid in the high temperature section. Therefore, the temperature of the second fluid flowing out from the second outlet can be effectively increased higher than 55° C., which is the limit of the temperature of the water flowing out from a conventional water heater; and consequentially the objects of raising up the temperature of the water flowing out from the water heater of the present invention and more power saving are achieved. Moreover, because the first and second pipes are contacted with each other by being disposed in a juxtaposition manner, the fluid flowing in one pipe is prevented from being polluted by the fluid flowing in the other pipe even when any one of the pipes is damaged and broken.

While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures. 

What is claimed is:
 1. A heat exchanging device configured to perform a heat exchange between a first fluid and a second fluid, the heat exchanging device comprising: a first pipe, comprising a first inlet and a first outlet thereby allowing the first fluid to flow in and out the first pipe through the first inlet and the first outlet, respectively; and a second pipe, comprising a second inlet and a second outlet thereby allowing the second fluid to flow in and out the second pipe through the second inlet and the second outlet, respectively, wherein the first pipe and the second pipe are contacted with each other by being disposed in a juxtaposition manner, a flowing direction of the first fluid in the first pipe is opposite to a flowing direction of the second fluid in the second pipe.
 2. The heat exchanging device according to claim 1, wherein both of the first and second pipes are oval-shaped pipes, the first pipe comprises a first contact surface, the second pipe comprises a second contact surface, the first contact surface and the second contact surface are contacted with each other in an extending direction of a short axis of each oval-shaped pipe.
 3. The heat exchanging device according to claim 1, wherein both of the first and second pipes are polygon-shaped pipes, the first pipe comprises a first contact surface, the second pipe comprises a second contact surface, the first contact surface and the second contact surface are contacted with each other.
 4. The heat exchanging device according to claim 1, wherein the first pipe comprises a first contact surface, the second pipe comprises a second contact surface, the first contact surface and the second contact surface are contacted with each other, the first contact surface comprises at least a recess, the second contact surface comprises at least a protrusion, the recess and the protrusion are contacted with each other.
 5. The heat exchanging device according to claim 1, wherein the first pipe comprises a first contact surface, the second pipe comprises a second contact surface, the first contact surface and the second contact surface are contacted with each other, the first contact surface comprises at least a protrusion, the second contact surface comprises at least a recess, the recess and the protrusion are contacted with each other.
 6. The heat exchanging device according to claim 1, wherein both of the first and second pipes have winding-and-bending structures.
 7. The heat exchanging device according to claim 1, further comprising an insulating layer configured to wrap the first and second pipes.
 8. The heat exchanging device according to claim 1, further comprising: a container, wherein the first and second pipes are disposed in the container; and an insulating layer, disposed in the container and configured to wrap the first and second pipes.
 9. A water heater, comprising: a heat exchanging device, comprising a first pipe and a second pipe, wherein the first pipe comprises a first inlet and a first outlet thereby allowing a first fluid to flow in and out the first pipe through the first inlet and the first outlet, respectively, wherein the second pipe comprises a second inlet and a second outlet thereby allowing a second fluid to flow in and out the second pipe through the second inlet and the second outlet, respectively, wherein the first pipe and the second pipe are contacted with each other by being disposed in a juxtaposition manner, a flowing direction of the first fluid in the first pipe is opposite to a flowing direction of the second fluid in the second pipe; and a heating unit, connected between the first outlet and the first inlet of the first pipe of the heat exchanging device.
 10. The water heater according to claim 9, wherein both of the first and second pipes are oval-shaped pipes, the first pipe comprises a first contact surface, the second pipe comprises a second contact surface, the first contact surface and the second contact surface are contacted with each other in an extending direction of a short axis of each oval-shaped pipe.
 11. The water heater according to claim 9, wherein both of the first and second pipes are polygon-shaped pipes, the first pipe comprises a first contact surface, the second pipe comprises a second contact surface, the first contact surface and the second contact surface are contacted with each other.
 12. The water heater according to claim 9, wherein the first pipe comprises a first contact surface, the second pipe comprises a second contact surface, the first contact surface and the second contact surface are contacted with each other, the first contact surface comprises at least a recess, the second contact surface comprises at least a protrusion, the recess and the protrusion are contacted with each other.
 13. The water heater according to claim 9, wherein the first pipe comprises a first contact surface, the second pipe comprises a second contact surface, the first contact surface and the second contact surface are contacted with each other, the first contact surface comprises at least a protrusion, the second contact surface comprises at least a recess, the recess and the protrusion are contacted with each other.
 14. The water heater according to claim 9, wherein the both of the first and second pipes have winding-and-bending structures.
 15. The water heater according to claim 9, further comprising an insulating layer configured to wrap the first and second pipes.
 16. The water heater according to claim 9, further comprising: a container, wherein the first and second pipes are disposed in the container; and an insulating layer, disposed in the container and configured to wrap the first and second pipes.
 17. The water heater according to claim 9, further comprising a receptacle configured to receive the second fluid flowing out from the second outlet of the second pipe. 